A conventional male clinch fastener, or clinch bolt, is permanently installed into a portion of a metal sheet so that the head becomes an integral part of the metal sheet and the threaded shaft extends upwardly from the sheet. The clinch bolt is installed by cold-forming the metal of the sheet or the head, rather than welding. The clinch bolt thus provides a threaded shaft with greater holding capacity than could be obtained by simply threading a conventional bolt through an opening in the sheet metal alone. Such a clinch bolt is commonly used in automobiles to provide a means for securing other objects to a metal sheet, for example.
One type of conventional clinch bolt is offered by Multifastener Corporation of Detroit, Mich. under the designation PIERCEFORM.RTM. SBK Stud. The bolt includes a head having an octagonal first portion adjacent the threaded shaft. A second portion of the head is a hollow tube with a smaller outer diameter than the first portion. As the bolt is inserted into an opening in the sheet, the sidewalls of the hollow tube are folded over and radially outwardly by a die to form a locking flange, while the octagonally shaped first portion is drawn into and flush with the sheet.
Unfortunately, the PIERCEFORM.RTM.SBK Stud is secured to the sheet by a-coining action or displacement of the parent material of the sheet. Thus, this clinch bolt may suffer from reduced pull-through and push-out performance.
The PIERCEFORM.RTM. Stud offered by Kean Manufacturing Corp. of Dearborn Heights, Mich. is a male fastener, or clinch bolt, having a threaded shaft extending outwardly from a generally cylindrical head, the head, in turn, is secured within a pilot, or collar, formed in the sheet. The PIERCEFORM.RTM. Stud forms, and then wraps around, a collar or pilot in the sheet into which the head has been pressed. A portion of the head is a hollow tube having walls that are folded over and radially outwardly by a die to form the locking flange. As the head is press fit into and through the sheet, edge portions of the sheet are bent downward to form the pilot for receiving the head of the bolt. A laterally extending flange on an end of the head adjacent the shaft is seated flush with the surface of the sheet. A relatively small number of circumferentially distributed ribs extend longitudinally along the first portion of the head to prevent rotational movement or torque-out of the nut.
The PIERCEFORM.RTM. Stud is a nondirectional clinch bolt, that is, it can be installed into a circular opening without concern for relative rotational orientation of the head of the bolt and the opening. In addition, this bolt offers improved performance characteristics over those conventional bolts described above which rely on the volumetric displacement or coining of parent material from the sheet.
Unfortunately, the PIERCEFORM.RTM. Stud suffers from a number of disadvantages including a relatively high cost of manufacture. Moreover, for a given bolt size, only a limited range of sheet material thicknesses and sizes of openings can be accommodated. In other words, since a predetermined portion of the tubular body is folded over for a given head size, the length of the pilot that can be effectively clamped between the first flange and the cold-formed flange must be accurately controlled.
The PIERCEFORM.RTM. Stud is also secured by the second metal flange which is formed by bending or folding a portion of the hollow head portion over the pilot formed in the sheet. This type of bending to cold-form the locking flange produces a relatively weak metal flange that may reduce pull-out performance.
In addition to male clinch fasteners, there are also female clinch fasteners, or clinch nuts. One such conventional clinch nut is available from RB&W Corporation of Mentor, Ohio, under the designation SPAC.RTM. nut. The SPAC.RTM. nut includes a back-tapered polygonal portion that is press fit into a slightly undersized opening in a sheet. The nut is locked into the sheet by a coining action as the sheet material flows to fill the space defined by the back-tapered portion, similar to the PIERCEFORM.RTM. SBK Stud described above. Also similar to the SPAC.RTM. nut are the STRUX-nut offered by Maclean-Fogg, and the HT-nut offered by NPR. Each of these clinch nuts relies upon the volumetric displacement of parent material from the sheet to fill an undercut or back-taper to create a kind of dove-tail joint between the fastener and the sheet. Unfortunately, such a clinch nut may not have sufficiently high performance characteristics, such as pull-through, push-out, and torque-out.
Yet another conventional clinch nut offered by the assignee of the present invention, requires that a hexagonal opening be punched into the sheet to accommodate the hexagonal body portion of the clinch nut. In other words, the clinch nut is a directional nut which requires proper orientation of the opening and proper alignment of the nut with the opening.
Another conventional clinch nut known commercially as the FLANGEFORM.TM. from RB&W, is disclosed in U.S. Pat. No. 4,018,257 to Jack entitled Self-Flanging Nut and Joint Construction. The FLANGEFORM.TM. clinch nut is similar to the PIERCEFORM.RTM. Stud as described above, and, accordingly, is subject to similar shortcomings.